Boolean analysis shows a high proportion of dopamine D2 receptors interacting with adenosine A2A receptors in striatal medium spiny neurons of mouse and non-human primate models of Parkinson's disease.

The antagonistic effect of adenosine on dopaminergic transmission in the basal ganglia indirect motor control pathway is mediated by dopamine D2 (D2R) and adenosine A2A (A2AR) receptors co-expressed on medium spiny striatal neurons. The pathway is unbalanced in Parkinson's disease (PD) and an A2AR blocker has been approved for use with levodopa in the therapy of the disease. However, it is not known whether the therapy is acting on individually expressed receptors or in receptors forming A2A-D2 receptor heteromers, whose functionality is unique. For two proteins prone to interact, a very recently developed technique, MolBoolean, allows to determine the number of proteins that are either non-interacting or interacting. After checking the feasibility of the technique and reliability of data in transfected cells and in striatal primary neurons, the Boolean analysis of receptors in the striatum of rats and monkeys showed a high percentage of D2 receptors interacting with the adenosine receptor, while, on the contrary, a significant proportion of A2A receptors do not interact with dopamine receptors. The number of interacting receptors increased when rats and monkeys were lesioned to become a PD model. The use of a tracer of the indirect pathway in monkeys confirmed that the data was restricted to the population of striatal neurons projecting to the GPe. The results are not only relevant for being the first study quantifying individual versus interacting G protein-coupled receptors, but also for showing that the D2R in these specific neurons, in both control and PD animals, is under the control of the A2AR. The tight adenosine/dopamine receptor coupling suggest benefits of early antiparkinsonian treatment with adenosine receptor blockers.

Brain ventricular enlargement in human and murine acute intermittent porphyria.

The morphological changes that occur in the central nervous system of patients with severe acute intermittent porphyria (AIP) have not yet been clearly established. The aim of this work was to analyze brain involvement in patients with severe AIP without epileptic seizures or clinical posterior reversible encephalopathy syndrome, as well as in a mouse model receiving or not liver-directed gene therapy aimed at correcting the metabolic disorder. We conducted neuroradiologic studies in 8 severely affected patients (6 women) and 16 gender- and age-matched controls. Seven patients showed significant enlargement of the cerebral ventricles and decreased brain perfusion was observed during the acute attack in two patients in whom perfusion imaging data were acquired. AIP mice exhibited reduced cerebral blood flow and developed chronic dilatation of the cerebral ventricles even in the presence of slightly increased porphyrin precursors. While repeated phenobarbital-induced attacks exacerbated ventricular dilation in AIP mice, correction of the metabolic defect using liver-directed gene therapy restored brain perfusion and afforded protection against ventricular enlargement. Histological studies revealed no signs of neuronal loss but a denser neurofilament pattern in the periventricular areas, suggesting compression probably caused by imbalance in cerebrospinal fluid dynamics. In conclusion, severely affected AIP patients exhibit cerebral ventricular enlargement. Liver-directed gene therapy protected against the morphological consequences of the disease seen in the brain of AIP mice. The observational study was registered at Clinicaltrial.gov as NCT02076763.

Adeno-Associated Viral Vectors as Versatile Tools for Parkinson's Research, Both for Disease Modeling Purposes and for Therapeutic Uses.

It is without any doubt that precision medicine therapeutic strategies targeting neurodegenerative disorders are currently witnessing the spectacular rise of newly designed approaches based on the use of viral vectors as Trojan horses for the controlled release of a given genetic payload. Among the different types of viral vectors, adeno-associated viruses (AAVs) rank as the ones most commonly used for the purposes of either disease modeling or for therapeutic strategies. Here, we reviewed the current literature dealing with the use of AAVs within the field of Parkinson's disease with the aim to provide neuroscientists with the advice and background required when facing a choice on which AAV might be best suited for addressing a given experimental challenge. Accordingly, here we will be summarizing some insights on different AAV serotypes, and which would be the most appropriate AAV delivery route. Next, the use of AAVs for modeling synucleinopathies is highlighted, providing potential readers with a landscape view of ongoing pre-clinical and clinical initiatives pushing forward AAV-based therapeutic approaches for Parkinson's disease and related synucleinopathies.

Cx3cr1-deficiency exacerbates alpha-synuclein-A53T induced neuroinflammation and neurodegeneration in a mouse model of Parkinson's disease.

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by the degeneration of dopaminergic neurons of the substantia nigra and the accumulation of protein aggregates, called Lewy bodies, where the most abundant is alpha-synuclein (α-SYN). Mutations of the gene that codes for α-SYN (SNCA), such as the A53T mutation, and duplications of the gene generate cases of PD with autosomal dominant inheritance. As a result of the association of inflammation with the neurodegeneration of PD, we analyzed whether overexpression of wild-type α-SYN (α-SYNWT ) or mutated α-SYN (α-SYNA53T ) are involved in the neuronal dopaminergic loss and inflammation process, along with the role of the chemokine fractalkine (CX3CL1) and its receptor (CX3CR1). We generated in vivo murine models overexpressing human α-SYNWT or α-SYNA53T in wild type (Cx3cr1+/+ ) or deficient (Cx3cr1-/- ) mice for CX3CR1 using unilateral intracerebral injection of adeno-associated viral vectors. No changes in CX3CL1 levels were observed by immunofluorescence or analysis by qRT-PCR in this model. Interestingly, the expression α-SYNWT induced dopaminergic neuronal death to a similar degree in both genotypes. However, the expression of α-SYNA53T produced an exacerbated neurodegeneration, enhanced in the Cx3cr1-/- mice. This neurodegeneration was accompanied by an increase in neuroinflammation and microgliosis as well as the production of pro-inflammatory markers, which were exacerbated in Cx3cr1-/- mice overexpressing α-SYNA53T . Furthermore, we observed that in primary microglia CX3CR1 was a critical factor in the modulation of microglial dynamics in response to α-SYNWT or α-SYNA53T . Altogether, our study reveals that CX3CR1 plays an essential role in neuroinflammation induced by α-SYNA53T .

History and future challenges of the subthalamic nucleus as surgical target: Review article.

For many years the subthalamic nucleus had a poor reputation among neurosurgeons as a result of the acute movement disorders that develop after its lesion or manipulation through different surgical procedures. However, this nucleus is now considered a key structure in relation to parkinsonism, and it is currently one of the preferred therapeutic targets for Parkinson's disease. The implication of the subthalamic nucleus in the pathophysiology of chorea and in the parkinsonian state is thought to be related to its role in modulating the basal ganglia, a fundamental circuit in movement control. Indeed, recent findings have renewed interest in this anatomical structure. Accordingly, this review aims to present a history of the subthalamic nucleus, evolving from the classic surgical concepts associated with the avoidance of this structure, to our current understanding of its importance based on findings from more recent models. Future developments regarding the relationship of the subthalamic nucleus to neuroprotection are also discussed in this review. © 2018 International Parkinson and Movement Disorder Society.

Receptor-heteromer mediated regulation of endocannabinoid signaling in activated microglia. Role of CB1 and CB2 receptors and relevance for Alzheimer's disease and levodopa-induced dyskinesia.

Endocannabinoids are important regulators of neurotransmission and, acting on activated microglia, they are postulated as neuroprotective agents. Endocannabinoid action is mediated by CB1 and CB2 receptors, which may form heteromeric complexes (CB1-CB2Hets) with unknown function in microglia. We aimed at establishing the expression and signaling properties of cannabinoid receptors in resting and LPS/IFN-γ-activated microglia. In activated microglia mRNA transcripts increased (2 fold for CB1 and circa 20 fold for CB2), whereas receptor levels were similar for CB1 and markedly upregulated for CB2; CB1-CB2Hets were also upregulated. Unlike in resting cells, CB2 receptors became robustly coupled to Gi in activated cells, in which CB1-CB2Hets mediated a potentiation effect. Hence, resting cells were refractory while activated cells were highly responsive to cannabinoids. Interestingly, similar results were obtained in cultures treated with ß-amyloid (Aß1-42). Microglial activation markers were detected in the striatum of a Parkinson's disease (PD) model and, remarkably, in primary microglia cultures from the hippocampus of mutant ß-amyloid precursor protein (APPSw,Ind) mice, a transgenic Alzheimer's disease (AD) model. Also of note was the similar cannabinoid receptor signaling found in primary cultures of microglia from APPSw,Ind and in cells from control animals activated using LPS plus IFN-γ. Expression of CB1-CB2Hets was increased in the striatum from rats rendered dyskinetic by chronic levodopa treatment. In summary, our results showed sensitivity of activated microglial cells to cannabinoids, increased CB1-CB2Het expression in activated microglia and in microglia from the hippocampus of an AD model, and a correlation between levodopa-induced dyskinesia and striatal microglial activation in a PD model. Cannabinoid receptors and the CB1-CB2 heteroreceptor complex in activated microglia have potential as targets in the treatment of neurodegenerative diseases.

Cannabinoid receptors CB1 and CB2 form functional heteromers in brain.

Exploring the role of cannabinoid CB(2) receptors in the brain, we present evidence of CB(2) receptor molecular and functional interaction with cannabinoid CB(1) receptors. Using biophysical and biochemical approaches, we discovered that CB(2) receptors can form heteromers with CB(1) receptors in transfected neuronal cells and in rat brain pineal gland, nucleus accumbens, and globus pallidus. Within CB(1)-CB(2) receptor heteromers expressed in a neuronal cell model, agonist co-activation of CB(1) and CB(2) receptors resulted in a negative cross-talk in Akt phosphorylation and neurite outgrowth. Moreover, one specific characteristic of CB(1)-CB(2) receptor heteromers consists of both the ability of CB(1) receptor antagonists to block the effect of CB(2) receptor agonists and, conversely, the ability of CB(2) receptor antagonists to block the effect of CB(1) receptor agonists, showing a bidirectional cross-antagonism phenomenon. Taken together, these data illuminate the mechanism by which CB(2) receptors can negatively modulate CB(1) receptor function.

Preferential expression of SCN1A in GABAergic neurons improves survival and epileptic phenotype in a mouse model of Dravet syndrome.

The SCN1A gene encodes the alpha subunit of a voltage-gated sodium channel (Nav1.1), which is essential for the function of inhibitory neurons in the brain. Mutations in this gene cause severe encephalopathies such as Dravet syndrome (DS). Upregulation of SCN1A expression by different approaches has demonstrated promising therapeutic effects in preclinical models of DS. Limiting the effect to inhibitory neurons may contribute to the restoration of brain homeostasis, increasing the safety and efficacy of the treatment. In this work, we have evaluated different approaches to obtain preferential expression of the full SCN1A cDNA (6 Kb) in GABAergic neurons, using high-capacity adenoviral vectors (HC-AdV). In order to favour infection of these cells, we considered ErbB4 as a surface target. Incorporation of the EGF-like domain from neuregulin 1 alpha (NRG1α) in the fiber of adenovirus capsid allowed preferential infection in cells lines expressing ErbB4. However, it had no impact on the infectivity of the vector in primary cultures or in vivo. For transcriptional control of transgene expression, we developed a regulatory sequence (DP3V) based on the Distal-less homolog enhancer (Dlx), the vesicular GABA transporter (VGAT) promoter, and a portion of the SCN1A gene. The hybrid DP3V promoter allowed preferential expression of transgenes in GABAergic neurons both in vitro and in vivo. A new HC-AdV expressing SCN1A under the control of this promoter showed improved survival and amelioration of the epileptic phenotype in a DS mouse model. These results increase the repertoire of gene therapy vectors for the treatment of DS and indicate a new avenue for the refinement of gene supplementation in this disease. KEY MESSAGES: Adenoviral vectors can deliver the SCN1A cDNA and are amenable for targeting. An adenoviral vector displaying an ErbB4 ligand in the capsid does not target GABAergic neurons. A hybrid promoter allows preferential expression of transgenes in GABAergic neurons. Preferential expression of SCN1A in GABAergic cells is therapeutic in a Dravet syndrome model.

Adeno-Associated Viral Vectors as Versatile Tools for Neurological Disorders: Focus on Delivery Routes and Therapeutic Perspectives.

It is without doubt that the gene therapy field is currently in the spotlight for the development of new therapeutics targeting unmet medical needs. Thus, considering the gene therapy scenario, neurological diseases in general and neurodegenerative disorders in particular are emerging as the most appealing choices for new therapeutic arrivals intended to slow down, stop, or even revert the natural progressive course that characterizes most of these devastating neurodegenerative processes. Since an extensive coverage of all available literature is not feasible in practical terms, here emphasis was made in providing some advice to beginners in the field with a narrow focus on elucidating the best delivery route available for fulfilling any given AAV-based therapeutic approach. Furthermore, it is worth nothing that the number of ongoing clinical trials is increasing at a breath-taking speed. Accordingly, a landscape view of preclinical and clinical initiatives is also provided here in an attempt to best illustrate what is ongoing in this quickly expanding field.

Recombinant porphobilinogen deaminase targeted to the liver corrects enzymopenia in a mouse model of acute intermittent porphyria.

Correction of enzymatic deficits in hepatocytes by systemic administration of a recombinant protein is a desired therapeutic goal for hepatic enzymopenic disorders such as acute intermittent porphyria (AIP), an inherited porphobilinogen deaminase (PBGD) deficiency. Apolipoprotein A-I (ApoAI) is internalized into hepatocytes during the centripetal transport of cholesterol. Here, we generated a recombinant protein formed by linking ApoAI to the amino terminus of human PBGD (rhApoAI-PBGD) in an attempt to transfer PBGD into liver cells. In vivo experiments showed that, after intravenous injection, rhApoAI-PBGD circulates in blood incorporated into high-density lipoprotein (HDL), penetrates into hepatocytes, and crosses the blood-brain barrier, increasing PBGD activity in both the liver and brain. Consistently, the intravenous administration of rhApoAI-PBGD or the hyperfunctional rApoAI-PBGD-I129M/N340S (rApoAI-PBGDms) variant efficiently prevented and abrogated phenobarbital-induced acute attacks in a mouse model of AIP. One month after a single intravenous dose of rApoAI-PBGDms, the protein was still detectable in the liver, and hepatic PBGD activity remained increased above control values. A long-lasting therapeutic effect of rApoAI-PBGDms was observed after either intravenous or subcutaneous administration. These data describe a method to deliver PBGD to hepatocytes with resulting enhanced hepatic enzymatic activity and protection against AIP attacks in rodent models, suggesting that the approach might be an effective therapy for AIP.

Recent Insights into the Pathogenesis of Acute Porphyria Attacks and Increasing Hepatic PBGD as an Etiological Treatment.

Rare diseases, especially monogenic diseases, which usually affect a single target protein, have attracted growing interest in drug research by encouraging pharmaceutical companies to design and develop therapeutic products to be tested in the clinical arena. Acute intermittent porphyria (AIP) is one of these rare diseases. AIP is characterized by haploinsufficiency in the third enzyme of the heme biosynthesis pathway. Identification of the liver as the target organ and a detailed molecular characterization have enabled the development and approval of several therapies to manage this disease, such as glucose infusions, heme replenishment, and, more recently, an siRNA strategy that aims to down-regulate the key limiting enzyme of heme synthesis. Given the involvement of hepatic hemoproteins in essential metabolic functions, important questions regarding energy supply, antioxidant and detoxifying responses, and glucose homeostasis remain to be elucidated. This review reports recent insights into the pathogenesis of acute attacks and provides an update on emerging treatments aimed at increasing the activity of the deficient enzyme in the liver and restoring the physiological regulation of the pathway. While further studies are needed to optimize gene therapy vectors or large-scale production of liver-targeted PBGD proteins, effective protection of PBGD mRNA against the acute attacks has already been successfully confirmed in mice and large animals, and mRNA transfer technology is being tested in several clinical trials for metabolic diseases.

Long-term neuroprotection and neurorestoration by glial cell-derived neurotrophic factor microspheres for the treatment of Parkinson's disease.

BACKGROUND: Glial cell-derived neurotrophic factor is a survival factor for dopaminergic neurons and a promising candidate for the treatment of Parkinson's disease. However, the delivery issue of the protein to the brain still remains unsolved. Our aim was to investigate the effect of long-term delivery of encapsulated glial cell-derived neurotrophic factor within microspheres. METHODS: A single dose of microspheres containing 2.5 µg of glial cell-derived neurotrophic factor was implanted intrastriatally in animals 2 weeks after a 6-hydroxydopamine lesion. RESULTS: The amphetamine test showed a complete behavioral recovery after 16 weeks of treatment, which was maintained until the end of the study (week 30). This effect was accompanied by an increase in dopaminergic striatal terminals and neuroprotection of dopaminergic neurons. CONCLUSIONS: The main achievement was the long-term neurorestoration in parkinsonian animals induced by encapsulated glial cell-derived neurotrophic factor, suggesting that microspheres may be considered as a means to deliver glial cell-derived neurotrophic factor for Parkinson's disease treatment.

Interactions between calmodulin, adenosine A2A, and dopamine D2 receptors.

The Ca(2+)-binding protein calmodulin (CaM) has been shown to bind directly to cytoplasmic domains of some G protein-coupled receptors, including the dopamine D(2) receptor. CaM binds to the N-terminal portion of the long third intracellular loop of the D(2) receptor, within an Arg-rich epitope that is also involved in the binding to G(i/o) proteins and to the adenosine A(2A) receptor, with the formation of A(2A)-D(2) receptor heteromers. In the present work, by using proteomics and bioluminescence resonance energy transfer (BRET) techniques, we provide evidence for the binding of CaM to the A(2A) receptor. By using BRET and sequential resonance energy transfer techniques, evidence was obtained for CaM-A(2A)-D(2) receptor oligomerization. BRET competition experiments indicated that, in the A(2A)-D(2) receptor heteromer, CaM binds preferentially to a proximal C terminus epitope of the A(2A) receptor. Furthermore, Ca(2+) was found to induce conformational changes in the CaM-A(2A)-D(2) receptor oligomer and to selectively modulate A(2A) and D(2) receptor-mediated MAPK signaling in the A(2A)-D(2) receptor heteromer. These results may have implications for basal ganglia disorders, since A(2A)-D(2) receptor heteromers are being considered as a target for anti-parkinsonian agents.

Expression of GPR55 and either cannabinoid CB1 or CB2 heteroreceptor complexes in the caudate, putamen, and accumbens nuclei of control, parkinsonian, and dyskinetic non-human primates.

Endocannabinoids are neuromodulators acting on specific cannabinoid CB1 and CB2 G-protein-coupled receptors (GPCRs), representing potential therapeutic targets for neurodegenerative diseases. Cannabinoids also regulate the activity of GPR55, a recently "deorphanized" GPCR that directly interacts with CB1 and with CB2 receptors. Our hypothesis is that these heteromers may be taken as potential targets for Parkinson's disease (PD). This work aims at assessing the expression of heteromers made of GPR55 and CB1/CB2 receptors in the striatum of control and parkinsonian macaques (with and without levodopa-induced dyskinesia). For this purpose, double blind in situ proximity ligation assays, enabling the detection of GPCR heteromers in tissue samples, were performed in striatal sections of control, MPTP-treated and MPTP-treated animals rendered dyskinetic by chronic treatment with levodopa. Image analysis and statistical assessment were performed using dedicated software. We have previously demonstrated the formation of heteromers between GPR55 and CB1 receptor (CB1-GPR55_Hets), which is highly expressed in the central nervous system (CNS), but also with the CB2 receptor (CB2-GPR55_Hets). Compared to the baseline expression of CB1-GPR55_Hets in control animals, our results showed increased expression levels in basal ganglia input nuclei of MPTP-treated animals. These observed increases in CB1-GPR55_Hets returned back to baseline levels upon chronic treatment with levodopa in dyskinetic animals. Obtained data regarding CB2-GPR55_Hets were quite similar, with somehow equivalent amounts in control and dyskinetic animals, and with increased expression levels in MPTP animals. Taken together, the detected increased expression of GPR55-endocannabinoid heteromers appoints these GPCR complexes as potential non-dopaminergic targets for PD therapy.

Expression of cannabinoid CB1 R-GPR55 heteromers in neuronal subtypes of the Macaca fascicularis striatum.

The cannabinoid CB1 receptor (CB1 R) is the most abundant G protein-coupled receptor in the central nervous system, consistent with the important role of endocannabinoids as neuromodulators. Cannabinoids also modulate the function of G protein-coupled receptor 55 (GPR55), which forms heteroreceptor complexes with the CB1 R in the striatum. The aim was to characterize cannabinoid CB1 R-GPR55 heteromers (CB1 R/GPR55Hets) in the basal ganglia input nuclei of nonhuman primates, Macaca fascicularis, both in projection neurons and interneurons, by the in situ proximity ligation assay. Striatal projecting neurons were identified by the retrograde neuroanatomical tracer, biotinylated dextran amine (BDA), injected into external or internal subdivisions of the globus pallidus. Triple immunofluorescent stains were carried out to visualize (1) BDA-labeled neurons, (2) CB1 R/GPR55Hets, and (3) striatal interneurons positive for choline acetyltransferase, parvalbumin, calretinin, or nitric oxide synthase. CB1 R/GPR55Hets were identified within both types of projection neurons as well as all interneurons except those that are cholinergic. Moreover, CB1 R/GPR55Hets were found specifically in the neuronal cell surface, and also in intracellular membranes. Further research efforts will be needed to confirm the intracellular occurrence of heteromers and their potential as therapeutic targets in diseases related to motor control imbalances, particularly within a parkinsonian context (with or without levodopa-induced dyskinesia).

Targeting CB1 and GPR55 Endocannabinoid Receptors as a Potential Neuroprotective Approach for Parkinson's Disease.

Cannabinoid CB1 receptors (CB1R) and the GPR55 receptor are expressed in striatum and are potential targets in the therapy of Parkinson's disease (PD), one of the most prevalent neurodegenerative diseases in developed countries. The aim of this paper was to address the potential of ligands acting on those receptors to prevent the action of a neurotoxic agent, MPP+, that specifically affects neurons of the substantia nigra due to uptake via the dopamine DAT transporter. The SH-SY5Y cell line model was used as it expresses DAT and, therefore, is able to uptake MPP+ that inhibits complex I of the respiratory mitochondrial chain and leads to cell death. Cells were transfected with cDNAs coding for either or both receptors. Receptors in cotransfected cells formed heteromers as indicated by the in situ proximity ligation assays. Cell viability was assayed by oxygen rate consumption and by the bromide-based MTT method. Assays of neuroprotection using two concentrations of MPP+ showed that cells expressing receptor heteromers were more resistant to the toxic effect. After correction by effects on cell proliferation, the CB1R antagonist, SR141716, afforded an almost full neuroprotection in CB1R-expressing cells even when a selective agonist, ACEA, was present. In contrast, SR141716 was not effective in cells expressing CB1/GPR55 heteromeric complexes. In addition, an agonist of GPR55, CID1792197, did not enhance neuroprotection in GPR55-expressing cells. These results show that neurons expressing heteromers are more resistant to cell death but question the real usefulness of CB1R, GPR55, and their heteromers as targets to afford PD-related neuroprotection.

Intratelencephalic corticostriatal neurons equally excite striatonigral and striatopallidal neurons and their discharge activity is selectively reduced in experimental parkinsonism.

Striatonigral and striatopallidal neurons form distinct populations of striatal projection neurons. Their discharge activity is imbalanced after dopaminergic degeneration in Parkinson's disease. Striatal projection neurons receive massive cortical excitatory inputs from bilateral intratelencephalic (IT) neurons projecting to both the ipsilateral and contralateral striatum and from collateral axons of ipsilateral neurons that send their main axon through the pyramidal tract (PT). Previous anatomical studies in rats suggested that IT and PT inputs preferentially excite striatonigral and striatopallidal neurons, respectively. Here we used electrophysiological criteria to identify them with antidromic stimulations. We show that the spontaneous discharge activity of IT neurons is depressed, whereas that of PT neurons is not affected in the rat cortex ipsilateral to 6-hydroxydopamine injection. However, our functional experiments do not support the hypothesis of a differential cortical input to striatal pathways. Firstly, although the conduction velocity of PT neurons is 4.6 times faster than that of IT neurons, identified striatopallidal and striatonigral neurons exhibit identical latencies of their spike responses to electrical stimulation of the ipsilateral cortex. Secondly, although PT neurons are ipsilateral, both striatal populations exhibit similar sensitivity to the stimulation of the ipsilateral and contralateral cortex. We suggest that IT neurons provide the main excitatory input to both striatal populations and that the corticostriatal PT input is weaker. Therefore, our functional data do not support our previous hypothesis that the deficit of IT neurons associated with the dopaminergic depletion might contribute to the striatal imbalance. This imbalance might rather result from intrinsic striatal mechanisms.

Usefulness of identifying G-protein-coupled receptor dimers for diagnosis and therapy of neurodegenerative diseases and of gliomas.

Immunochemical detection of G-protein-coupled receptors (GPCRs) in cells and tissues was a technical challenge for years. After the discovery of formation of GPCR dimers/trimers/tetramers in transfected cells, a most recent challenge has been to confirm receptor-receptor interactions in natural sources. The occurrence of dimers or higher order oligomers is important from a therapeutic point of view, mainly because their physiology/pharmacology is different from those of individual receptors. On the one hand, pathophysiological factors need to count more on GPCR dimers than on individual receptors. On the other hand, the expression of dimers, trimers, etc. may change in pathological conditions and/or along the course of a disease. This review will focus on G-protein-coupled receptor dimers, on how to detect them by novel histological techniques and on how the detection may be used in diagnosis and therapy of ailments of the central nervous system, for instance in neurodegenerative diseases and gliomas.

Alterations in Gene and Protein Expression of Cannabinoid CB2 and GPR55 Receptors in the Dorsolateral Prefrontal Cortex of Suicide Victims.

Recent studies point to the cannabinoid CB2 receptors (CB2r) and the non-cannabinoid receptor GPR55 as potential key targets involved in the response to stress, anxiety, and depression. Considering the close relationship between neuropsychiatric disorders and suicide, the purpose of this study was to evaluate the potential alterations of CB2r and GPR55 in suicide victims. We analyzed gene and protein expression of both receptors by real-time PCR and western blot, respectively, in the dorsolateral prefrontal cortex (DLPFC) of 18 suicide victims with no clinical psychiatric history or treatment with anxiolytics or antidepressants, and 15 corresponding controls. We used in situ proximity ligation assay to evaluate whether the receptors formed heteromeric complexes and to determine the expression level of these heteromers, also assessing the co-expression of heteromers in neurons, astroglia, or microglia cells. CB2r and GPR55 gene expressions were significantly lower (by 33 and 41%, respectively) in the DLPFC of suicide cases. CB2r protein expression was higher, as were CB2-GPR55 heteroreceptor complexes. The results also revealed the presence of CB2-GPR55 receptor heteromers in both neurons and astrocytes, whereas microglial cells showed no expression. We did not observe any significant alterations of GPR55 protein expression. Additional studies will be necessary to evaluate if these alterations are reproducible in suicide victims diagnosed with different psychiatric disorders. Taken together, the results suggest that CB2r and GPR55 may play a relevant role in the neurobiology of suicide.

Brain delivery of microencapsulated GDNF induces functional and structural recovery in parkinsonian monkeys.

Glial cell line-derived neurotrophic factor (GDNF) remains the most potent neurotrophic factor for dopamine neurons. Despite its potential as treatment for Parkinson's disease (PD), its clinical application has been hampered by safety and efficacy concerns associated with GDNF's short in vivo half-life and with significant brain delivery obstacles. Drug formulation systems such as microparticles (MPs) may overcome these issues providing protein protection from degradation and sustained drug release over time. We therefore sought to evaluate the efficacy and safety of GDNF delivered via injectable biodegradable MPs in a clinically relevant model of PD and to investigate the mechanism contributing to their beneficial effects. MPs were injected unilaterally into the putamen of parkinsonian monkeys with severe nigrostriatal degeneration. Notably, a single administration of the microencapsulated neurotrophic factor achieved sustained GDNF levels in the brain, providing motor improvement and dopaminergic function restoration. This was reflected by a bilateral increase in the density of striatal dopaminergic neurons 9 months after treatment. Moreover, GDNF was retrogradely transported to the substantia nigra increasing bilaterally the number of dopaminergic and total neurons, regardless of the severe degeneration. GDNF-MP injection within the putamen elicited no adverse effects such as immunogenicity, cerebellar degeneration or weight loss. MPs are therefore a safe, efficient vehicle for sustained protein delivery to the brain, supporting the therapeutic benefit of GDNF when encapsulated within MPs for brain repair. Overall, these findings constitute important groundwork for GDNF-MP clinical development.